The present invention relates to a method of injection-moulding in which an injection nozzle is separated from a mould every moulding-cycle, and to an injection moulding machine for carrying out the method.
Generally, the moulding cycle of an injection moulding machine comprises the processes of injection, holding pressure, cooling, weighing, and opening and closing the mould. These processes are repeatedly carried out in this order. When the moulding is carried out with an injection nozzle kept in contact with the mould, heat from the nozzle is transferred to the mould, prolonging the cooling time. That is, the time taken for the moulding cycle cannot be reduced. Thus, an injection moulding machine is known in which the nozzle is separated from the mould every moulding cycle, so that the transfer of heat between the nozzle and the mould is kept to a minimum.
FIG. 5 shows an example of a known injection moulding machine. The injection moulding machine comprises an injection unit 100 having an injection nozzle 101, a mould 102, and a mould opening-closing unit 103. Furthermore, the injection moulding machine is provided with a hydraulic cylinder 104 which causes the injection unit 100 to move towards or away from the mould 102 so that the nozzle 101 comes into contact with, or is separated from, the mould 102.
However, to operate the hydraulic cylinder 104, hydraulic pressures must be switched by valve-operation. Thus, the switch-over operation is slow. For this reason, the moulding cycle cannot be achieved. Moreover, the hydraulic cylinder 104 needs to be operated synchronously with the opening and closing of the moulds. It is necessary to control the injection moulding machine 104 accurately at high speed. It is problematic that the mechanism for controlling the machine becomes complicated.
In the injection moulding machine of the related art, the mould opening-closing unit 103, which is a mechanism for opening and closing the moulds, and the hydraulic cylinder 104, which is a nozzle-touch mechanism, are driven independently of each other. Thus, the hydraulic cylinder 104 is caused to operate following opening and closing of the moulds at high speed with much difficulty. Therefore, problems are caused in that heat from the nozzle tip is readily transferred; defects in fluidity of resin such as so-called cold slag are easily caused, and the qualities of the moulded product become unstable.
The invention aims to address the above mentioned problems.
According to the invention there is provided a method of injection-moulding, comprising the steps of: operating a first mould (31) to move in a mould clamping direction and come into contact with a second mould (30); further operating the first mould (31) to move in the mould clamping direction while the first mould (31) is in contact with the second mould (30) and bring the second mould (30) into contact with an injection nozzle (11); operating the first mould (31) to move in the mould clamping direction integrally with the second mould (30) and the injection nozzle (11) until the second mould (30) reaches a retention position, while the second mould (30) is in contact with the injection nozzle (11); injecting a plasticated resin into the first and second moulds (31, 30) through the injection nozzle (11), while the second mould (30) is maintained at the retention position; operating the first mould (31) to move in a mould-opening direction after the injection to separate the second mould (30) from the injection nozzle (11); and further operating the first mould (31) to move in the mould-opening direction to separate the first mould (31) from the second mould (30).
The invention also provides an injection moulding machine comprising: a mould unit (B) and an injection unit (A) having an injection nozzle for injecting a plasticated resin into the mould unit (B) through the injection nozzle (11), the mould unit (B) comprising a mould opening-closing means, a first mould (31) drivable for opening or closing by the mould opening-closing means, a second mould (30) operable together with the first mould to define a cavity therebetween and to be brought into contact with the injection nozzle (11), a first guide means (39) for guiding the second mould (30) so that the second mould (30) can be moved in the mould opening-closing direction, a stroke-regulating means (40) for regulating the length of stroke in the mould opening-closing direction of the second mould (30), and a first energizing means (41) for energizing the second mould (30) in the direction of the first mould (31), and the injection unit (A) comprising a second guide means for guiding the injection nozzle so that the injection nozzle (11) can be moved in the mould opening-closing direction, a stopper means for defining a limit position of movement of the injection nozzle (11) in the direction of the second mould (30) and a second energizing means (9) for energizing the injection nozzle (11) in the direction of the second mould (30), wherein the length of stroke S1 of the second mould (30) caused by the stroke regulating means (40) is set to be equal to or larger than the gap S2 between the second mould (30) and the injection nozzle (11) defined when the moulds are open.
The objects of the present invention have the advantage that the injection-moulding nozzle can be separated from a mould every moulding cycle by means of a simple mechanism and can correspond to opening and closing the mould at high speed.
In an first aspect of the invention, the first mould, when moved in the mould clamping direction, comes into contact with the second mould, and then the first and second moulds are moved together in the direction of the injection nozzle. The first mould is further moved in the mould clamping direction, so that the second mould comes into contact with the injection nozzle. In this state, the first mould is moved until the second mould reaches the retention position. Therefore, clamping of the first and second moulds and moreover, contact of the second mould with the injection nozzle can be securely achieved. In this state, a plasticated resin is injected into the first and second moulds through the injection nozzle.
Thereafter, when the first mould is moved in the mould-opening direction, the first and second moulds and the injection nozzle integrally move away. Then, the injection nozzle stops, and is separated from the second mould. The first mould is further moved in the mould-opening direction. The second mould then stops. The first and second moulds are then opened, and the moulded product therebetween is removed.
In the first aspect of the invention described, the stroke length S1 of the second mould is set to be larger than the gap S2 between the second mould and the injection nozzle. Therefore, the clamping and opening of the first and second moulds and also the contact and separation of the injection nozzle from the second mould can be carried out only by moving the first mould in the mould-clamping direction and in the mould-opening direction. Thus, the injection nozzle can be securely separated from the mould every shot, following the clamping and opening of the moulds. Accordingly, thermal conduction from the injection nozzle to the mould can be suppressed, and the cooling time for the moulds can be reduced. As a result, the time required for each moulding cycle can be reduced. Moreover, the tip of the nozzle and its vicinity can be maintained at high temperature, since the time when the tip of the injection nozzle is in contact with the mould can be reduced.
Moreover, according to the present invention, the second mould, while it is in contact with the injection nozzle, is further moved by a predetermined length in the mould-clamping direction. Therefore, the second mould can be securely brought into contact with the injection nozzle, and leakage of a plasticated resin can be prevented, even if thermal expansion and dimensional errors occur.
In a second aspect of the invention, the method of injection-moulding of the first aspect of the present invention can be applied by using a simple mechanism. In addition to the mould opening and closing means, the machine comprises the first and second moulds, the first guiding means for guiding the second mould so that the second mould can be moved in the mould opening and closing direction, the stroke-regulating means for regulating the length of stroke in the mould opening-closing direction of the second mould, and the first energizing means for energizing the second mould in the direction of the first mould, the second guiding means for guiding the injection nozzle in such a manner that the injection nozzle can be moved in the mould opening-closing direction, the stopper means for defining a limit position of the injection nozzle at which the movement of the injection nozzle in the direction of the second mould is limited, and the second energizing means for energizing the injection nozzle in the direction of the second mould. The stroke length S1 of the second mould caused by the stroke regulating means is set to be equal to or larger than the gap S2 between the second mould and the injection nozzle defined when the moulds are in the open state. Thus, for the purpose of moving the injection unit, no special operational mechanism is required. The injection nozzle can be securely separated from the mould, even if the moulds are opened and closed at high speed.
Spring, a hydraulic cylinder, a motor, and other possibilities may be used as the first and second energizing means. Where springs are used, the mechanism for opening and closing the moulds is the sole power source required for the springs. Thus, an injection moulding machine can be provided which is small in size and inexpensive.